Traditionally, dyestuffs have been available as dry powders which have numerous inherent disadvantages. Such powders are dusty, resulting in health hazards due to worker inhalation of the dust and leading to cross contamination of one dyestuff by dust from another. Additionally, these powders require considerable energy and effort to dissolve them into the aqueous dye baths typically used in the textile dyeing industry. Furthermore, this powder form cannot be readily adapted for automated metering and handling making their utilization by the end user labor intensive and therefore inefficient compared to the potential offered by modern materials handling technology. Finally, the drying of dyestuffs from the wet filter cake form in which they are recovered from their synthesis batch is an energy intensive step. Therefore, the need to reduce dyestuffs to this dried, powder form significantly increases the cost of their production.
In response to these difficulties, a significant number of dyestuffs of various classes have been formulated in liquid form. Some types, such as those disclosed in U.S. Pat. No. 4,071,312 have simply been dissolved in water. However, some types of dyes either have insufficient solubility to permit the preparation of commercially significant concentrations or have a tendency to react with the water or solvents commonly used in dyestuffs formulations, if not immediately, during storage or shipment. Among the former type of dyes are the anionic dyes which are formulated into dispersions in U.S. Pat. No. 3,770,371 by the addition of sufficient salt to render these dyes substantially insoluble. A further development disclosed in U.S. Pat. No. 4,110,073 has been to utilize concentrations of anionic dyestuffs well above their normal solubility in water in combination with high levels of selected surfactants including lignin sulfonates.
Both the solution and dispersion techniques have been applied to some fiber reactive dyes, i.e. those dyes carrying groups capable of forming a covalent bond with the textile substrate, particularly cellulose, being dyed. The solution approach has generally been restricted to those dyes requiring fairly high temperatures (in excess of about 60.degree. to 80.degree. C.) to effect fixation to the textile substrate and such dyes are accordingly known as "hot dyers" and "warm dyers," respectively. The application of this solution approach to hot dyers and warm dyers in combination with careful pH control by buffers is disclosed in U.S. Pat. No. 4,072,463. The low room temperature reactivity of the fiber fixing groups of these dyes in combination with the careful pH control is evidently sufficient to avoid significant hydrolysis of these fiber reactive groups by the water solvent. The dispersion approach has been applied to both such "hot dyers" in U.S. Pat. Nos. 3,770,371 and 4,110,073 as well as to the "cold dyers" in U.S. Pat. No. 4,264,323.
These "cold dyers" are of particular interest because of their ability to fix on textile substrates at moderate temperatures by adjustment of the dye bath to alkaline conditions. However, their high reactivity with the hydroxyl groups of cellulose or other textile substrates which enables this low temperature dyeing also makes them highly susceptible to hydrolysis whenever exposed to water including the period of time before they are added to an aqueous dye bath for final utilization. In fact, the fiber reactive groups of these dyestuffs undergo significant hydrolysis when their initial synthesis is conducted in aqueous media.
U.S. Pat. No. 4,264,323 has proposed preparing dispersions of such "cold dyers" in saturated solutions of the very same dyestuffs. Although these formulations are evidently storable for relevantly long periods of time at "room temperature" nothing is reported about their stability under the range of thermal conditions actually experienced in the field. In particular, it is not possible to confidently conclude that such dispersions would resist both hydrolysis and settling or agglomeration upon exposure to the thermal cycling which would occur from the variation in day and night temperatures in a good part of the United States. Even though these formulations carefully exclude any dispersants or other additives which bear groups potentially reactive with their fiber fixing groups there remains the significant possibility of hydrolysis with their aqueous medium upon exposure to elevated temperatures during warehousing or transportation in the summer months.
German Patent Publication No. 2,843,015 has proposed formulations of such "cold dyers" in aqueous solutions of neutral or weak acid salts to give dispersions of the dyestuffs. There does not appear to be any discussion of possible hydrolysis with the water suspending medium but only a discussion at page 5, lines 25 to 29 that the disclosed procedure is advantageous because the primary and secondary alcohols typically used in formulating liquid dyes are reactive with the fiber fixing groups of these dyes. The dispersions are reported to settle within a few weeks but to be readily redispersible with stirring. It is also reported that the dispersions must be added to "hot" water or heated with steam to dissolve them in aqueous dye baths. These dispersions are also reported to be "stable" against heat and frost.
Therefore, there is a need for storage stable liquid concentrated dispersions of "cold dyeing" water soluble fiber reactive dyes. These dispersions need to display stability to both hydrolysis of their fiber reactive groups and settling or agglomeration of their dispersed dyestuff particles. They should also be readily flowable, preferably without substantial agitation. During storage under field conditions, these dispersions should not undergo a significant degradation of their dyeing potential by hydrolysis of their fiber reactive groups and therefore a loss of their ability to chemically bond with suitable textile substrates. Furthermore, they should be capable of storage for prolonged periods without experiencing any significant settling or agglomeration and at worst only, mild agitation should be required to render them fully fluid.
The field conditions actually experienced by commercially utilized dyestuffs include thermal cycling which can be a particularly severe test of the stability of such dispersions. Such dispersions may typically see a wide variation in temperature from day to night when being transported or warehoused. If the dispersed dyestuff dissolves to any significant degree at the elevated daytime temperatures on cooling to night temperatures, it may precipitate onto the dispersed dyestuff particles causing an increase in the average particle size (known as "Ostwald ripening"). A significant change in the average particle size may result in the dispersion settling or agglomerating.
This problem is of particular concern with regard to these "cold dyeing" fiber reactive dyes because of their normally high solubility in water. It is desirable that such dyestuffs readily dissolve with only mild agitation at mild temperatures when the dispersion is added to an aqueous dye bath and thus greatly diluted. This "kinetic solubility" is obtained both from the thermodynamic solubility of the dyestuff molecule and from a small dispersed particle size. Unfortunately, both factors favor "Ostwald ripening" of the dispersion.
Surprisingly, it has been found that aqueous dispersions of small particle size (under 100 microns) cold dyeing, water soluble, fiber reactive dyestuffs can be prepared in commercially attractive concentrations to have superior kinetic solubility in the ultimate dye bath and still display superior resistance to both hydrolysis of its fiber reactive group and settling or agglomeration of its particles by the judicious addition of an electrolyte, such as common salt, and a dispersant such as sodium ligninsulfonate.